Download Biology 105

Biology 105
Chapter 51: Development
Pages 1106-1126
Student Outcomes
Describe the processes involved in fertilization
Trace the generalized pattern of early
development of the embryo from zygote through
early cleavage
Identify the significance of gastrulation in the
developmental process
Student Outcomes
• Define Organogenesis and the three germ
layers
Fertilization
• Process of joining of egg and sperm to
form a zygote. Known as conception.
• Spermatogenesis and oogenesis
• Involves 4 events:
Fertilization events
1. sperm contacts the egg and recognition
occurs
2. sperm or sperm nucleus enters the egg
3. egg becomes activated, beginning
developmental changes
4. sperm and egg nuclei fuse.
Polyspermy
the fertilization of the egg by more than
one sperm. Results in extra
chromosomes and is usually lethal.
Zygote
Is totipotent
Cleavage occurs shortly after fertilization
Cell goes through 2 cell, 4 cell, 8 cell stages,
etc.
At the 32 cell stage – known as morula, and
eventually a blastula
Morula-Blastula
• 32 cell stage – Usually at this stage when
entering the uterus. These cells are known
as blastomeres. Continued mitotic
divisions (Cleavage) results in a Blastula
(hollow ball of cells with a blastocoel)
Gastrulation
Blastula becomes a gastrula which forms the 3 germ
layers:
– Ectoderm
– Mesoderm
– Endoderm
– The three germ layers will give rise to organogenesis - the
formation of organs. Notochord, brain and spinal cord are the
first organs to develop
Ectoderm
– Outer layer – Will give rise to:
• Nervous system and sense organs
• Outer layer of skin, nail and hair
• Pituitary
Mesoderm
Middle layer – Will give rise to
skeleton
muscles
circulation
excretory
reproduction
dermis
Endoderm
• Will give rise to:
– Lining of the digestive tube
– respiratory
Implantation
Occurs on about the 7th day of embryo
development. It imbeds in the endometrium of
the uterus.
Human Development Timeline
• Fertilization
• 24 hours – 2 cell stage
• 3 days – Morula travels through fallopian tubes
•
•
and reaches uterus
7 days – implantation
17 days – tissue that will give rise to heart is
differentiating, neural plate is formed
Human development continued
• 25 days – primitive eye and ear visible,
heart begins to beat
• 4 weeks – limb buds appear, brain division
forming
• 8 weeks – muscles differentiation, embryo
capable of movement, sex organs can be
seen, bone is ossifying
Human development continued
3 months- sex can be determined
4 months – face takes on a ‘human’ form with eyes,
ears and nose
Third trimester – known as a fetus, tremendous growth
of the body, cerebrum growth is rapid
266 days – Birth
All Development Stages
• Gametogenesis-Fertilization
• Embryo: Cleavage-Morula-BlastulaImplantation-Gastrula-Organogenesis
• Fetus: 2 month-Birth (organogenesis)
• Birth-Neonate-Infant-Child-AdolescentYoung adult-Middle aged adult-Elderly
adult
• Death
Multiple Births
• Twins
– Identical - one egg, one sperm, seperation
after the 2 cell stage or the inner cell mass
divides into 2 separate masses (monozygotic)
– Non identical - two eggs, two sperm
(dizygotic)
– Conjoined - Same as identical, seperation
does not occur completely.
Births cont.
• Triplets – Identical - one egg, one sperm
– Non identical - more than one egg and sperm